A data processing device (e.g., a mobile phone, a desktop computer, a laptop computer, a notebook computer, a netbook, a smart television, a gaming console) may have a display unit on which video frames or images are rendered. For the convenience of a user of the data processing device, subtitles may be overlaid on the video frames or the images to enable the user comprehend audio content associated therewith. When color parameters (e.g., color brightness, color saturation) of the video frames or the images are comparable to those of the subtitles, the user may find it difficult to discern the video frame/image content and/or the subtitle content.